(1) Summary of the Invention
The present invention relates to a syringe which on the plunging stroke of a piston injects a liquid through a needle into an animal and which refills with the liquid upon retraction of the piston. In particular, the present invention relates to a syringe which is filled from behind at an end opposite the needle from a bottle which is connected by a tube to the back of the syringe, thereby the name "back-fill syringe".
(2) Prior Art
U.S. Pat. No. 2,374,368 to Mejia discloses a valved syringe with an open supply reservoir. U.S. Pat. No. 1,995,971 to Dowling and U.S. Pat. No. 3,353,537 to Knox et al describe two valve syringes. U.S. Pat. No. 4,204,539 to Brugge discloses a hand operated apparatus with two valves. None of these patents describe a "stick"syringe with automatic refilling of the syringe from a refill bottle which is valved to allow only air inlet so that the device can be used under "field" conditions with large animals such as cattle. Where the bottle is open, the bottle can not be carried on the person of the operator.
Another syringe apparatus is described in Russian Patent No. 933,101 to Timoshin. This patent describes a single-hand operation veterinary instrument for injecting livestock which incorporates systems for automatic sterilization of the injection needle and for disinfection and marking of the injected area with a colored disinfectant solution. A syringe, injection needle holder and ejector, and a bellows operated pump are mounted on a pistol-type grip body. The inlet of the syringe is connected by plastic tubing and a two-way valve to a bottle of veterinary preparation. The outlet is connected by plastic tubing and a sleeve to the injection needle. The inlet of the bellows is connected by plastic tubing to a bottle of colored disinfectant solution. The outlet is connected by plastic tubing and a sleeve to a spray on the injection needle holder. The ejector comprises a spring loaded striker which is activated by a trigger lever, the length of travel being controlled by stops. This device is complicated and has external hoses across the pistol grip body of the syringe which can easily become detached or damaged.